Polyurethane dormant mix and method of forming a foamed polyurethane



United States Patent 01 fice 3,391,094 Patented July 2, 1968 ABSTRACT OF THE DISCLOSURE A dormant dry mix consisting of a diisocyanate, a polyol, a dicarboxylic acid, an organo metallic catalyst, a Lewis acid as an esterification accelerator and a wetting agent for producing a foamed polyurethane by heating to a temperature of about 75 to 80 C. wherein the water to foam the polyurethane is formed in situ without the addition of water liberating compounds such as hydrates.

The dormant dry mix is particularly useful under outer space conditions in producing foamed polyurethane but can be used under ordinary atmospheric conditions. For example, the present invention is used in rigidization of structures used in outer space and also for providing thermal insulation for said structures.

CROSS REFERENCE TO RELATED APPLICATION The application is a continuation-in-part of application Serial No. 395,339 filed Sept. 9, 1964, and now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to (a) a method of producing a foamed polyurethane at a relatively low temperature and (b) the dormant dry mix used in the above method.

2. Description of the prior art According to the prior art, the preparation of foamed polyurethane material has employed water for the production of carbon dioxide for blowing or foaming the polymer. It will be apparent that liquid water could not be introduced into a solid reactant system in the hard vacuum of a space environment which is the contemplated use for the polyurethane foam made by the process and from the mix of the present invention.

A representation of the actual chemical reactions in conventional polyurethane formations that have been available heretofore and that include the reaction of water with an isocyanate prepolymer is illustratively:

The above representation of the chemistry for the formation of a urethane polymer is the same reaction mechanism for etiher a liquid or a solid system with the exception that in a liquid prepolymer system, the water is added in the liquid state. In the case of a solid reactant system, the water must be chemically combined in some manner so that it is releasable and available to enter into the reaction. Various approaches have been used to incorporate combined water into a solid reactant urethane system.

One such method was to absorb water into molecular sieves. Molecular sieves are micro-sized particles of silica. Still another attempted method to make water available in a solid reactant system was the use of compounds with high water of hydration content. See for example, column 2, lines 46-58 of US. Patent No. 2,895,926 and column 2, lines 21-31 of US. Patent No. 3,226,344. None of the aforementioned procedures proved satisfactory because high temperatures were required for the sieves and for the hydrated compounds to release their water content.

This approach was especially undesirable for production of a polymer under vacuum conditions since the reactants vaporized due to the high temperatures required to release the water from the hydrated compounds. In addition, the water obtained from the hydrate is released in the vapor phase and escapes too rapidly for utilization in the reaction. According to the present invention, the water formed in situ from esterification during the reaction of the mix provides the necessary water for foaming.

In addition, the prior art discloses that the previously developed solid urethane formulations have not only necessitated relatively high temperatures to initiate reaction but have required the continuous application of heat to maintain the reaction in order to completely polymerize and cure the material. A solid polyurethane system which does not develop sufficient exothermic heat to sustain the polymerization reaction to completion has inherent disadvantages and drawbacks, such as having limited areas of application due to the need for the entire amount or volume of prepolymer to be exposed to a heat source until the material has expanded and cured and being diflicult to use in a space environment for the rigidization of space structures due to the high temperature requirements.

SUMMARY OF THE INVENTION The present invention is directed to (a) a composition of matter which consists of a diisocyanate, a polyol, a dicarboxylic acid, an organo metallic catalyst, a Lewis acid as an esterfication accelerator and a wetting agent, and (b) a method of producing a foamed polyurethane by heating the above composition at about -80 C. whereby there is initiated an exothermic, self sustaining chemical reaction consisting of esteriiication, polymerization, foaming due to the water liberated by said esterificaiton, and curing.

One of the objects of the present inveniton is to provide a polyurethane foam useful in an outer space environment. A further object of this invention is to provide a dormant dry mix in which an exothermic reaction is initiated at a relatively low temperature and goes to completion without the continuous application of heat. Another object of this invention is to effect foaming of the polyurethane by the water formed during the esterification step of the general reaction of the composition thereby eliminating the need for certain chemical compounds, such as hydrates, in the dormant mix as a source of water for foaming the polyurethane. Additional objects will be apparent from the description of the preferred embodiment which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENT More specifically, this invention comprises a charge 3 4 of premixed powdered and dry solid reactants that are develops sufficient exothermic heat to sustain itself to inert, as mixed under laboratory conditions and as stored completion. for indefinite periods of time, as long as the tempera- This invention comprises the provision of an exothermic ture remains below its melting point of between 70 and self-sustaining chemical reaction from solid reactants all 75 C. (158 to 167 F.). The inert dry mix is actuated 5 of which are dry powders, to produce a foamed polyby temperature alone without any additives or agents. urethane, either in a space environment or under at- The dormant dry mix may be caused to expand at will mospheric conditions. The water for the reaction is obin an environmental vacuum in the order of 5 lO tained from the joining and the esterification of a dimm/Hg, or under limited pressure up to at least one hyclric or a polyhydric alcohol and a dicarboxylic oratmosphere, to form a physically rigid structure, or a ganic acid, using a Lewis acid such as aluminum chlostructure that is of a desired flexibility depending on the ride as an esterification accelerator. With the esterificacomposition of the particular mix. tion accelerator, less heat is required to initiate esterifica- In the making of a desired structure, the dormant tion. As the polyhydroxy ester is formed, subsequent mix is placed, for example, in a mold and the temperapolymerization occurs between the ester and the diisoture of the mix 'is raised to its melting point. At its meltcyanate with the water produced from the esterification ing point, the inert mix begins an exothermic reaction being used in the polymerization reaction for the prothat is thermally sustained to completion at between 150- duction of carbon dioxide. 225 C. (302 to 436 F.). A schematic equation for the chemical reaction process,

In view of the nature of this reaction, the mixed mawith R and R indicating appropriate radicals, is: terial is adaptive to the formation of solid structures in A1013 the vacuum of outer space without the addition of re- 2 R RC 0 actants. The material shapes up with or without the re- (dihydric (dicarboxylic alcoholor diol) organic acid) quired use of a mold due to the surface tension of the material during its transition from solid fine particles fi* "fi 21110 through a liquid phase and then into a structurally con- 2: o t-inuous solid unitary body. (mm diol) The solid reactant system is composed illustratively of a solid diisocyanate, a solid dihydric, trihydric, or

polyhydric alcohol, a solid organic dior poly-carboxylic 0 acid, a surfactant or wetting agent, a solid organo metal- 30 0eyanate) (di 11c catalyst or amine catalyst, and a Lewis acid as an O O accelerator for the esterification of the alcohol-organic H H H acid. The water which is produced from the esterifica- 0 0 tion of the acid and alcohol is not only used in the (isocyanateterminated Prepolymer) (prepolymer)' (water from esterification) H H (-N-fi}-0-R-o fi-lV-(fo-R0fi-N1R)u nGOz (polyurethane) polymerization process of the dihydroxy ester but in ef- One such formulation which reacts according to the fecting foaming of the polyurethane. preceding reaction mechanism and which produces a rela- It should be noted that this invention is applicable tively high density foam at atmospheric conditions and to the production of a foamed polyurethane polymer in 50 a relatively low density foam in a high vacuum environa space environment or at laboratory atmospheric conment, is as follows:

Material Structure Molecular Equlv. Melting Equiv. Gms.

Weight Weight Point. 0. Used Adipic acid HO0C(CHQ)4COOH 140.14 73. 07 151-153 0.3 22.0 Trimethylolpropanc CH CH2C(CHgOH)3 135.0 45.0 58.0 0.6 27.0

n Methylene bis (4-pl1enyl isocyanate) o (ENG-g-ONOO 248.0 124. 0 100 0.4 50.0

Organo metallic catalysL. 1.0 Aluminum chloride 2.0 Tween 21 (wetting agent) 3. 0

ditions, such as at a pressure of one atmosphere and The above listed formulation produces an exothermic a temperature of about 20 C., from a composition of $5 self-sustaining chemical reaction once the composition is solid reactants using Lewis acids such as aluminum chloraised to a temperature of 75 C. by exposure to ride (A101 as an esterification and polymerization aca thermal energy source. The above formulation procelerator. duces a semi-rigid foam. However, the dicarboxylic acid The reactants, which constitute the present one-package and the diol or polyol can be substituted with other dipremixed composition are dormant until they are exposed 70 carboxylic acids and diols of either longer or shorter earto 'a thermal energy source at a temperature approximatbon chains to yield either a flexible or a rigid foam. The ing the melting point of the specific formulation. The organo metallic catalyst in the above formulation illustrareactants may be selected such that they will provide a tively is dibutyl tin-di-2 ethyl hexoate. Tween is a generic composition that will react at various temperature ranges. term for a series of non-ionic surface-active agents which After the thermal initiation of the reaction, the reaction are polyoxyalkalene derivatives of hexitol anhydride partial long chain fatty acid esters. Tween 21 is a poly-oxyalkalene derivative of sorbitan monolaurate which is an oily liquid at 25 C., has a specific gravity of 1.051.10, a flash point of 410 R, and a fire point of 495 F.

It is to be understood that the reactants and the procedural steps that are described herein have been submitted as being a successfully operative illustrative embodiment of the present invention and that limited modifications may be made therein without departing from the spirit and the scope of the present invention. The last three items in the above formulation are open to adjustment in their quantities, as related to the ambient pressures at which the material is to be foamed. The above formulation gave satisfactory results at the pressure of S 1()- mm. Hg. A satisfactory foam is obtained with the AlCl eliminated at atmospheric pressures.

Numerous changes and modifications will be apparent to those skilled in the art without departing from the inventive concept and only the claims define the mete s and bounds of this invention.

What I claim is:

1. A solid composition of matter for producing a foamed polyurethane and which is capable of producing a self-sustaining exothermic chemical reaction upon being heated to about 75 to 80 C. of said composition consisting of about 50 parts by weight of a methylene bis (4-phenyl is-ocyanate), about 27 parts by weight of trimethylolpropane, about 22 parts by weight of adipic acid, about 1 part by Weight of dibutyltin-di-2 ethyl hexoate as a catalyst, about 2 parts by Weight of aluminum chloride as an esterification accelerator, and about 3 parts by Weight of polyoxyethylene derivative of sorbitan monolaurate as a wetting agent.

2. A process for producing a foamed polyurethane comprising the steps of 1) mixing a solid composition consisting of about parts by weight of methylene bis (4-phenyl isocyanate), about 27 parts by weight of trimethylol propane, about 22 parts by Weight of adipic acid, about 1 part by weight of dibutyltin-di-Z ethyl hexoate as a catalyst, about 2 parts by weight of aluminum chloride as an esterification accelerator, and about 3 parts by Weight of a polyoxyalkalene derivative of sorbitan monolaurate as a wetting agent, and thereafter (2) heating the composition to a temperature between and C., whereby there is initiated an exothermic, self-sustaining chemical reaction wihch consists of (a) esterification, (b) polymerization, (c) foaming due to the water liberated by said esterification, and (d) curing, said reaction continuing to completion without further addition of heat.

References Cited UNITED STATES PATENTS 2,895,926 7/1959 Rappaport et a1. 3,057,824 10/1962 Le Bras et al. 3,226,344 12/1965 Schwartz et a1.

OTHER REFERENCES Chemical Abstracts, vol. 52, No. 19, p. 16281 (c), Oct. 10, 1958.

DONALD E. CZAJA, Primary Examiner.

M. B. FEIN, Assistant Examiner. 

